Conversion of analog images into digital data has become widespread for a variety of applications, including storing, manipulating, transmitting and displaying or printing copies of the images. For example, images captured in photographic media are converted to digital data and stored on compact discs for readout and display as a video image, as exemplified by the KODAK.RTM. Photo-CD system, or reproduced employing various types of color printers. In order to convert the photographic image into a set of digital line data, the film image frame is transported through a film scanning station past, and illuminated in each scan line with a linear light beam of uniform, diffuse illumination, typically produced by a light integrating cavity or integrator.
With respect to light integrators per se, various configurations are known in the art of still and telecine film scanners and typically include an elongated cylindrical integrating cavity having diffusely reflective walls and an output slit which extends parallel to the longitudinal axis of the cylindrical integrating cavity. Improved light integrators for such uses are disclosed in commonly assigned U.S. Pat. Nos. 4,868,383 and 5,241,459, and also include a light source for generating an intense beam of light and an optical system for directing the beam end-wise into the cavity through an input port that is offset from the longitudinal axis of the cavity and is angularly offset from the input port by less than 180.degree.. The introduced light is diffusely reflected in the cavity and is emitted from the elongated slit as a uniform intensity, diffuse line of light. In the U.S. Pat. No. '459 patent, the light source and optical system introduce high intensity light through the input port at an angle that is not parallel to the longitudinal axis or the exit slit of the cavity. Such light integrators produces a line of diffuse, Lambertian light which has a uniform linear and angular distribution, and excellent line scan results can be obtained over a wide range of operating conditions.
The light transmitted through the illuminated scan line of the image frame is focused by a lens system on a linear CCD array, image detector which typically produces three primary color light intensity signals for each image pixel that are digitized and stored. The digitized signal values for each scan line may be formatted to a standard for video recording and display and stored on compact disc or magnetic media. Such film scanners take a variety of forms, and the various common aspects of film image frame digitizing, particularly line illumination and linear CCD array-based digitizers, are described in greater detail in commonly assigned U.S. Pat. No. 5,155,596.
In order to perform line scanning of each image frame of photographic negative filmstrips, it is necessary to provide an accurate film transport mechanism to transport a filmstrip into a scanning gate and hold the image frame flat in alignment with a scanning aperture. Typically, the linear CCD array and scanning light beam are stationary, so that the light beam illuminates a line of the filmstrip image frame, and a line of digitized data is stored. The scanning gate containing the filmstrip image frame is incrementally moved or translated line-by-line by a stepping drive motor until the entire image frame is digitized. Then a new image frame is positioned and flattened for scanning and digitizing. Such a scanning and digitizing system for Photo-CD conversion is embodied in the KODAK.RTM. PIW Model 2400 Photo-CD scanner system marketed by the assignee of this application.
In this film scanner, the scanning plane is vertical and the stationary scanner components are oriented horizontally. The filmstrip is advanced past the stationary scanner components in a first pass for scanning the image frames at a low resolution sufficient to provide a video display of each image frame on a monitor for viewing by the operator. The color balance of the scanned and digitized image pixel data is automatically adjusted to the color balance characteristics of the video display. The operator may further adjust the displayed color balance or tone and intensity of the color display while viewing the result of the adjustments until satisfied, whereupon the adjustment factors for that image frame are stored. The orientation of the image may also be stored with the digitized data so that the CD player can rotate the image data 90.degree. for display as a video image at the same aspect that the image was captured by the photographer.
As each image frame is scanned in this first pass, the scanned image frames of the vertically oriented filmstrip are advanced into a stationary take-up chamber. The take-up chamber is provided within the scanner to temporarily hold the filmstrip and isolate it from other apparatus that it could catch on and to keep it clean. After all image frames are scanned, the trailing end of the filmstrip is retracted from the chamber and advanced in the reverse direction into the scanning gate one frame at a time. Then each image frame is scanned at high resolution for digitizing the image as a field of data associated to the data derived in the low resolution scan of the same image frame. The filmstrip is transported out the exit of the translation stage for removal by the operator when scanning of all frames is completed.
In order to scan positive color transparencies in mounts, i.e. slides, employing common components of the same film scanner station, it is necessary for the operator to manually replace the film translation stage and substitute a slide translation stage in the Model 2400 Photo-CD scanner. The replacement is tedious and mechanical breakdowns are possible in attempting the exchange of the translation stages.
For efficiency and high resolution, the film scanning registration planes of the film image frames in the respective scanning gates are held very close to the linear light emitting slit or surface of the light integrator. The light integrator remains stationary in its horizontal orientation. It is not desirable to remove and replace the integrator each time the slide scanning gate must be positioned in or taken out of the scanning station, since doing so may lead to misalignment or damage.